Inhaling certain gases can dramatically alter the sound of a person’s voice. This effect highlights the connection between gas properties and the physics of sound. Understanding the underlying science provides insight into why some gases cause voices to become higher pitched, while others lead to a noticeably deeper tone.
Unveiling the Deep-Voice Gas
The gas responsible for making a voice sound significantly deeper is sulfur hexafluoride (SF6). This gas is notably heavier than the air we breathe. SF6 has a density of approximately 6.12 grams per liter, considerably higher than air’s density of about 1.225 grams per liter. This makes sulfur hexafluoride roughly five to six times denser than ordinary air.
This property contrasts with gases like helium, which is significantly less dense than air. While helium makes voices high-pitched by allowing sound to travel faster, SF6 achieves the opposite effect due to its greater density. The difference in density between these gases is the primary factor influencing vocal pitch.
The Science Behind the Deep Voice
When sulfur hexafluoride is inhaled, it fills the respiratory tract. Sound waves travel through this new, denser medium. The speed of sound through SF6 is considerably slower than through air, moving at about 120 meters per second compared to air’s 335 meters per second. This reduced speed directly influences how the sound produced by the vocal cords is transmitted.
The vocal cords vibrate at their normal frequency, unaffected by the gas. However, the slower speed of sound in SF6 means the resonant frequencies of the vocal tract, which acts like a resonating chamber, are lowered. As sound waves travel more slowly through the dense gas, they are effectively “stretched out.” This results in a lower perceived pitch and a deeper voice, akin to a slowed-down recording.
Safety and Practical Uses
While the voice-altering effect of sulfur hexafluoride can be interesting, understanding safety considerations is important. SF6 is generally considered non-toxic and inert. However, inhaling pure SF6 can pose a risk because it displaces oxygen in the lungs. This can lead to asphyxiation if not performed carefully or if too much is inhaled without sufficient oxygen replenishment.
Beyond recreational demonstrations, sulfur hexafluoride has various practical applications. It is widely used in the electrical industry as an insulating gas in high-voltage equipment, such as circuit breakers and switchgear, due to its high dielectric strength. In the medical field, SF6 is employed in ophthalmology, particularly in retinal detachment surgeries, where its density helps maintain the eye’s shape during healing. It is also used as an ultrasound contrast agent and for pulmonary function tests.